Loudspeakers generally comprise a frame, a motor structure, a diaphragm, a lower suspension or spider and a surround or upper suspension. In one type of speaker, the motor structure includes a permanent magnet sandwiched between a top plate and a back plate, with a pole piece centrally mounted on the back plate so that both the top plate and magnet are concentrically disposed about the pole piece. A magnetic gap is formed between the pole piece and top plate within which a voice coil is axially movable. The voice coil consists of a hollow, cylindrical-shaped former including an inner surface and an outer surface which mounts a winding of wire having a voice coil lead. Lead wires are connected at one end to the voice coil lead of the wire winding, and at their other end to electrical terminals which are fixed to the frame. The voice coil is mounted within the magnetic gap by the upper and lower suspensions and the diaphragm. One end of the diaphragm is connected to the upper suspension, which, in turn, is mounted to the upper end of the frame. The lower suspension or spider is connected at one end to a seat or spider plateau formed in the frame. The free ends of the diaphragm and spider are mounted to the outer surface of the former of the voice coil and support it for axial movement within the magnetic gap. In the course of operation, electrical energy is supplied via the lead wires to the voice coil causing it to axially move within the magnetic gap. The voice coil, diaphragm, upper suspension and spider collectively form a “moving assembly” which reciprocates as a unit with the excursion of the voice coil.
Loudspeakers of the type described above are typically manufactured as follows. The motor structure is assembled by gluing the magnet in between the top plate and back plate, and then the frame and motor structure are connected together. Using precision shim stock positioned between the voice coil former and pole piece, the voice coil is located within the motor structure at the appropriate height. In most instances, one end of each lead wire is attached to the voice coil lead of the wire winding of the voice coil before it is placed in position relative to the pole piece.
As noted above, the voice coil is suspended within the magnetic gap of the motor structure by the upper suspension or surround and the spider. First, the inner diameter of the spider is slid down over the former of the voice coil to a height which allows its outer diameter to lay flat on the spider plateau formed in the frame. The inner diameter of the spider is then glued to the voice coil former and its outer diameter is glued to the spider plateau. With the spider in position, the body of the diaphragm is slid over the voice coil former. In most instances, the diaphragm and surround are supplied by the manufacturer as a single, interconnected unit. Typically, a foot or flange of the diaphragm rests on the joint connection between the spider and the voice coil so that the diaphragm is placed at the appropriate height relative to the voice coil. The diaphragm is glued to the voice coil, and the surround is glued to a flange at the top of the frame. The lead wires are then threaded through holes in the diaphragm and extended toward the frame. A dust cap is often attached to the diaphragm, over its open center, to prevent dust and other debris from entering the voice coil or motor structure. Finally, the free end of each lead wire is attached to the electrical terminals on the frame, which are usually attached to the frame in a prior assembly operation.
Once the voice coil is positioned on the pole piece of the motor structure, all other assembly operations noted above must be performed within the loudspeaker frame because fixtures are employed to obtain proper alignment of the remaining parts. Depending upon the physical size of the loudspeaker being assembled, it is difficult to fit one's hands into the loudspeaker frame to work. Although many frames are formed with openings or “windows,” these openings are usually of limited size particularly in small speakers. This constraint can make installing the lead wires a real challenge, and it is extremely difficult to accurately gauge the length of the lead wires within the frame.
Several problems arise if the lead wires are not properly installed in a speaker. If a lead wire is too short, it can be drawn too tight during high excursions of the voice coil risking damage to the moving assembly and the lead wire connections. On the other hand, lead wires which are too long create a large arc between the voice coil and electrical connections at the frame. Long lead wires can dynamically misbehave during diaphragm movement, potentially contacting the diaphragm or spider, and create undesirable noise. Further, not unlike a guitar string, the suspended length of the lead wire can have its own resonance behavior. Consequently, if the length of the lead wire is not carefully considered during the design phase of the speaker and then properly installed, a loudspeaker can be rendered nearly useless by the undesirable noises created.
There have been attempts in the prior art to manage the dynamic behavior of speaker lead wires. At the frame, lead wires are very often soldered to electrical terminals with a small amount of flexible glue being applied at the location where the lead wire leaves the terminal. The purpose of the flexible glue is to attempt to control the angle at which the lead wire exits the terminal, to provide at least some motion damping and to relieve stress at the connection of the lead wire to the terminal. At the other end of the lead wires, flexible glue is typically used where the lead wires extend through holes in the diaphragm in an attempt to control the angle of the lead wire at that location and also to assist with management of the dynamic behavior of the lead wire, including stress relief at the lead wire connection to the voice coil. Unfortunately, applying flexible glue consistently at either end of the lead wires is very difficult since these operations must be performed by hand within the interior of the speaker frame.